1d, 2d, 3d Now 4d Barcodes.

To increase the capacity of two dimensional barcodes a third dimension, color can be added. These 3d codes are available already as noted in a previous post Color C Code and now researchers are looking at adding a fourth dimension, time. The image below shows what they may look like and this paper provides further information, Unsynchronized 4D Barcodes (pdf).